4 Metrics You Should Add to Your Email Reporting - Litmus
Briefly

We frequently use data to help us understand our own audience. By combining data from a sentiment tracker with overall email engagement, you can easily understand your audience sentiment versus inferring it from open or click-through rates.
Keeping track of engagement times can help you get insights on how your subscribers interact with your email after they open and before they click.
Read at Litmus
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